With many good properties, the polyester fiber has conventionally been one of the most widely used synthetic fibers, and in recent years, in particular, efforts in the apparel industry have resulted in the development of modified or improved materials with excellent feel, which are generally called "new synthetic fibers". These "new synthetic fibers" have been accepted in the market because of their novel excellent texture, totally different from other conventional materials, which has been achieved by a polyester fiber production method that combines an advanced technique to produce raw thread and a high-level processing step to manufacture a woven/knitted product. These "new synthetic fibers" with excellent texture, however, have some problems in terms of costs and quality stability because they need a complicated combination of an advanced raw thread production technique and a high-level processing step. In particular, several types of raw threads have to be subjected to false twisting and filament-combining to achieve the new feature of excellent texture, and furthermore union-twisting and union weaving may be carried out to achieve high value added, which leads to very high prices. After a series of similar products has been placed on the market, consumers now tend to call for products with different texture, resulting in demand for further improvements in terms of appearance and functional properties.
To solve these problems, a woven/knitted product with surface variations, for example, can be produced by twisting and false twisting. This method, however, requires large costs and has difficulty in achieving a novel surface texture. In addition, the necessity of false twisting makes it impossible to produce a stretchable woven/knitted product. Some techniques, including the use of polyurethane-based elastic fiber, are available to impart stretchability to a woven/knitted product, but they require large costs and cannot produce products with a novel surface texture. There are some known techniques in which knitted products with surface variations are produced by using a conjugate yarn consisting of two different polymer components aligned side by side. In some efforts, furthermore, such products are false-twisted to achieve stretchability. These techniques, however, require many processes that need large costs, and resultant products tend to suffer from a poor hand.
Japanese patent publications JP-B51-37376 and JP-B57-25650 have proposed methods for producing bulky yarn, bulky woven products, and bulky knitted products, in which an extended conjugate yarn consisting of polyethylene terephthalate and copolyester is subjected to relaxation-heat treatment under very small tension to achieve crimping. Though able to achieve crimping stably, these techniques have been found to have difficulty in providing woven/knitted products with surface variations and stretchability.
When such conventional fabric is produced using a shrinkable straight thread as raw material, the resultant product has no surface variations and no stretchability. If said straight thread is subjected to addition of twist and used to produce a woven/knitted product, surface variations can be developed by heating the product to form wrinkles due to the effect of untwisting torque, but it is still difficult to make it stretchable. Though actually having crimps, conventional false-twisted yarn has no ability to develop additional crimps over the existing ones. In the case of false-twisted yarn, furthermore, the crimps are too fine, and are not aligned in phase. As a result, such fabric can be bulky and less transparent, but cannot have sufficient surface variations or stretchability.
The conventionally known technique that uses a conjugate yarn consisting of two polyester polymer components with different heat-shrinking properties combined in parallel with each other or in a core-sheath configuration can produce a woven/knitted product in which a certain degree of stretchability develops in some structural portions where restraining force is small. However, when the yarn is in the form of an aggregate of filaments, the resultant fiber can be shrunk, but will be poor in the ability to develop crimps after overcoming the restraining force of the structures in the woven/knitted product. As in the case of conventional material produced from a single-component polyester multifilament yarn, said product suffers from transparency and poor bulkiness, and does not have surface variations. Thus, the present inventors carried out earnest studies to develop a method to produce a woven/knitted product with both surface variations and stretchability, and achieved the present invention after finding that a desired woven/knitted product can be produced by starting with a material with half-developed crimps, which is prepared by providing latent crimps at floated portions around the intersections of warp and weft in a woven product or in the loops in a knitted product, followed by allowing the latent crimps to develop into full ones.
There is also increased demand for woven/knitted products that are produced from synthetic products and have such features as resilience as well as lightweight properties and stretchability which are not found in most natural fiber products. A solution to this is proposed in Japanese patent publication JP-A5-247757, but it is difficult to produce lightweight products because the crimps in the filaments developed by crimping and false twisting of conjugate fiber are not aligned in phase, making it difficult to allow large voids to develop. To provide lightweight products, Japanese patent publications JP-A62-85048 and JP-A4-289219 have proposed the use of hollow fiber. In this technique, the hollow proportion of the hollow fiber is the key factor to weight reduction. If the hollow proportion in the hollow fiber is increased, however, the diameter of the fiber has also to be increased to allow high-level processing to be performed effectively. For instance, false twisting performed to enhance the stretchability can result in squashing of hollow parts, or breakage of hollow parts while the clothing product is worn. Thus, it has been widely thought that with the conventional techniques, it is difficult to produce products with both stretchability and lightweight properties at reduced processing costs.
In another existing technique, several different raw threads are used to develop novel effects in woven/knitted products, and composite false twisting and composite combined filament processing are carried out to develop additional valuable properties. This technique, however, tends to require very large electric power costs for false twisting and air processing.
Such additional costs required for composite processing can be absorbed in the case of such thick fabric products as suits and coats that sell at relatively high prices. In the case of such thin fabric products as blouses and shirts that cannot sell at high prices, the additional costs cannot be absorbed, so it is important to minimize the processing costs. To develop a woven product with value added, on the other hand, it is important to use several different threads as composite yarn to achieve a synergistic effect, and development efforts have been made to provide techniques to reduce the costs required for composite processing.
In another proposed technique that uses a false-twisted composite yarn to enhance its value, a two- or multiple-layer structure is formed to contribute to imparting novel texture as well as stretchability as a functional property. Japanese patent publication JP-A5-247757 proposes subjecting a polyester conjugate yarn to false twisting and crimping first, followed by a filament-combining process. This technique, however, requires large costs for an increased number of processes for false twisting and air filament-combining, and resulting products tend to be poor in hand.